Angular and linear position sensors are widely used in automatic control systems as feedback-sensing devices in one or more control loops of the system. Rotary position sensors are adaptable for many applications. For example, in the automotive industry, rotary position sensors are applied for monitoring or providing active control of many vehicle born systems such as active suspension, body height position sensing, steering wheel and throttle position sensing, throttle control, seat and window positioning systems, door and body panel closure systems and accessory actuation systems, to name a few.
Rotary position sensors frequently employ a magnetic field and a galvanomagnetic sensing element, such as a Hall effect device or a magneto resistor located within the magnetic field. To detect rotational movement as between a first article (such as for example a rotatable throttle shaft of an air control valve) and a second article (such as for example a stationary base), the magnetic field is oriented transverse in relation to the axis of rotation of the first article, and the galvanomagnetic sensing element is located inside the magnetic field. The member providing the magnetic field is connected to one of the articles, and the galvanomagnetic sensing element is connected to the other article. As the articles rotate relative to each other, the galvanomagnetic sensing element is caused to change its angular position relative to the magnetic field direction, resulting in a change of output signal from the galvanomagnetic sensing element responsive to its angle with respect to the magnetic field direction. This change in signal is indicative of the angular position as between the first and second articles.
As described in U.S. Pat. No. 6,489,761, position sensors with digital outputs provide discrete position information only. Position sensors (Philips KMA200, Micronas HAL855, etc.) having digital outputs, such as Pulse Width Modulated-PWM or Serial Protocol Interface-SPI, can also be used for providing continuous position information. This position information can then be used to drive electromechanical devices. Non-contact, magnetic switches provide discrete position information only. Non-contact, magnetic sensors (of the kind “switching halls” or “switching MRs”), typically used for engine cam/crank and/or ABS applications, also provide quasi-digital outputs where a high indicates a tooth (or slot) and a low indicates a slot (or tooth) on the ferromagnetic target wheel being sensed. Alternatively, the sensor of the present invention provides continuous position information in either digital or analog (ratio-metric) mode, depending on the application.
A typical prior art analog position sensor can provide both position information and outputs that can be used to drive an electric motor or similar electro-mechanical devices. Many of these devices are driven by sinusoidal excitations as a function of position. Consequently, an analog position sensor having an output that varies sinusoidally with position could be used to generate absolute angular positions as, for example, an electrical power steering system to measure the angle of rotation of the steering wheel, and/or reference signals to produce the desired sinusoidal phase drive currents and voltages to drive electric motors and other similar electromechanical devices.
The operational principle of an angle encoder sensor is based upon the property of Hall plates or semiconductor magneto resistors, collectively referred to herein as magnetosensitive devices, to sense only the normal component of the magnetic field passing through them, in the case of the hall devices, or the parallel component, in the case of the magneto resistive devices. The operation of Hall plates will be described below, keeping in mind that magneto resistors operate in a similar manner but are sensitive to direction changes of the incident magnetic field parallel to the face of such devices. Consequently, if a constant and uniform magnetic field is rotated in a plane perpendicular to the surface of a magnetosensitive device, the output signal will vary as the cosine of the angle between the direction of the incident magnetic field lines and the line normal to the surface of the device. It is preferred in this regard, that the magnetosensitive device be linear in its response to change in direction of the incident magnetic field, such as that provided by Hall plates. However, magneto resistors operating in their linear region (ie. under saturation) can also be used. In addition, operation over any ambient temperature range may require temperature compensated magnetosensitive devices. Also, it should be noted that included by the term “magnetosensitive devices” are ferromagnetic magneto resistors, including giant magneto resistor (GMR) sensors.
Accordingly, what remains needed is a compact, robust, highly accurate and inexpensive rotary position sensor, which is easily adaptable for varied applications and can be easily manufactured in large quantities while maintaining quality and consistency of performance.